This invention relates to a magnetic bubble memory driving circuit for generating a rotating magnetic field which is utilized to propagate magnetic bubbles.
In order to propagate magnetic bubbles between propagation patterns, it is necessary to apply a plain rotating field in a magnetic film in which the magnetic bubbles are present.
FIG. 1 is a perspective view showing a coil block for generating a rotating magnetic field, in which an X coil 1 and a Y coil 2 are arranged at right angles and a bubble memory chip, not shown, which is contained in these coils. The magnetic field produced by the X coil 1 is directed in the direction of arrow X and the magnetic flux generated by the Y coil 2 is directed in the direction of arrow Y so that when a sine wave current is passed through the X coil 1 and a sine wave current lagged by 90.degree. is passed through the coil 2, a rotating magnetic field having a circular magnetic field locus and rotating in the counterclockwise direction will be formed.
This system, however, requires an oscillating circuit to produce sine wave currents, and there is a trend, in recent years, toward use of direct current voltage which is applied to the coils to generate triangular current by the inductance of the coils.
FIGS. 2a and 2b show waveforms of the triangular currents flowing through X coil and Y coil respectively, and FIG. 3 shows the magnetic field locus. When a triangular current is passed through the X coil and a triangular current lagged by 90.degree. is passed through the Y coil, a rotating magnetic field having a square magnetic field locus will be produced.
FIG. 4 shows an example of a driving circuit which has hitherto been used for producing such a triangular current, and FIGS. 5a, 5b and 5c show the time chart of this circuit. In FIG. 4, reference numerals 3, 4, 5 and 6 designate transistors and 7, 8, 9 and 10 diodes which are connected as shown. When transistors 3 and 6 are turned on simultaneously, a source of DC designated at + E applies a voltage to the X coil 1 with its left side positive and right side negative so that current flows in the direction of arrow i. This direction is called the positive direction. Since the applied DC voltage is constant, the current increases linearly due to the inductance of the X coil 1. When transistors 3 and 6 are turned off after a predetermined time, the electromagnetic energy that has been stored in the coil 1 decreases and current flows to the DC source through diodes 8 and 9, this current decreasing linearly. This decreasing time is substantially equal to the interval in which transistors 3 and 6 have been turned on. Accordingly, a positive triangular current will be produced during an interval twice on the "ON" period of transistors 3 and 6. Subsequently, when transistors 4 and 5 are simultaneously turned on, a voltage is impressed across the X coil in the opposite direction so that current flows through this coil in the opposite direction which increases linearly. When transistors 4 and 5 are turned off after a predetermined time, the electromagnetic energy that has been stored in the X coil 1 decreases and current flows to the source via diodes 7 and 10 which decreases linearly. Accordingly, a negative triangular current will be obtained during an interval twice the "ON" time of transistors 4 and 5. Thereafter, this operation is repeated to produce a continuous triangular current. These states are shown by FIGS. 5a through 5c, in which FIG. 5a shows the ON-OFF states of transistors 3 and 6, FIG. 5b the ON-OFF states of transistors 4 and 5, and FIG. 5c shows the triangular current flowing through the X coil 1 and identical to FIG. 2a. The triangular current flowing through Y coil 2 can be produced by a similar circuit.
The above-described triangular wave currents having a phase difference of 90.degree. flow through X coil 1 and Y coil 2 and the magnetic fields produced thereby are synthesized to form a rotating magnetic field adapted to propagate magnetic bubbles.
However, in the prior art magnetic bubble driving circuit, one set of driving circuits each including 4 transistors and 4 diodes has been necessary for each coil, so that as the number of the magnetic bubble elements increases, the number of the coils increases and the number of the driving circuits also increases, thus increasing the cost and occupied space.